Marine production risers may be associated with a floating vessel or floating platform where ocean wave conditions cause the platform to heave and relative movement occurs between the upper end portion of the riser system and the platform.
Various systems have been employed for connecting the upper end of a production riser pipe to a platform. Individual risers; that is, a single riser pipe extending from the seabed to the floating platform, have often been provided with slip joints just below the platform to allow such relative movement of the platform and the upper end portion of the riser pipe. In some systems, a ball joint is provided at the platform to accommodate relative angular movement of the riser pipe with respect to the platform. The upper end portion of such prior riser systems were connected to constant tension lines for support of the riser pipe.
Some prior proposed marine production riser systems have included a plurality of riser pipes terminated at a floating platform. In such instances, each of the plurality of riser pipes were supported and tensioned individually. As a result, the space above the termination of such a plurality of riser pipes was cluttered with many cables and various equipment. It was difficult to work in such space, particularly when work was performed on perhaps only one of the riser pipes.
In addition, such prior proposed termination of the plurality of riser pipes at the platform employed means for tensioning each riser pipe individually. It will be understood that each riser pipe may be carrying a fluid having different characteristics with respect to internal pressure, weight, density, and temperature. As a result of the fluid conducted by each riser pipe, the tension imposed upon such a riser pipe may vary. In prior proposed systems, each riser pipe was tensioned individually and individual support of a plurality of such pipes presented difficulties because of constantly varying conditions.